People who have been infected with one strain can be infected with another. Sequential infections put them at increased risk for dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS), which can be fatal.

DHF is a very dangerous form of dengue infection. It can be fatal if unrecognized and not properly treated. DHF is caused by infection with the same viruses that cause dengue fever. It can cause internal bleeding and a drop in blood pressure, followed by shock and sometimes death. Fluid in the blood can leak through the skin and into the spaces around the lungs and belly. With good medical management, mortality due to DHF can be less than 1 percent.

Dengue shock syndrome (DSS) is dengue hemorrhagic fever with signs of circulatory failure. The fatality rate can be as low as 0.2 percent with early treatment, but once shock has set in, the mortality rate can be 12 percent to 44 percent.

Are there any treatments for dengue?

Right now, there are no specific medications to treat its symptoms and no vaccine. However, there are several vaccines in development:

Dr. Anna Durbin, an associate professor in international health at the Johns Hopkins Bloomberg School of Public Health, is conducting clinical trials in Baltimore -- and later this summer in Brazil -- with an experimental dengue vaccine created by the National Institutes of Health. She is also part of the Pediatric Dengue Vaccine Initiative (PDVI), an international consortium of scientists, drug manufacturers and public health institutions.

The pharmaceutical company Sanofi Aventis, which has been testing its ChimeriVax dengue vaccine in tropical countries, predicts it will have a dengue vaccine on the market by 2015.

Another potential dengue vaccine is being jointly developed by GlaxoSmithKline and several U.S. agencies, including the CDC and Armed Forces Research Institute of Medical Sciences.

What can I do if I get dengue?

You can use pain relievers containing acetaminophen (Tylenol), but should avoid aspirin, aspirin-containing medications or those containing ibuprofen (Advil, Motrin), or naproxen (Aleve, Naprosyn). Rest, drink plenty of fluids to prevent dehydration, avoid mosquito bites while you have a fever and consult a physician.

How can I reduce my risk of dengue infection?

Prevention is key and that starts with avoiding mosquito bites if you live in or are traveling through an area where there is dengue.

The best way to reduce mosquito bites is to eliminate where mosquitoes lay their eggs, such as containers that hold water in and around the home. Don't keep water outdoors in pet bowls. Cover water storage barrels. Beware of standing water inside your home in vases holding fresh flowers; clean these at least once weekly.

Adult mosquitoes like to bite inside as well as around homes during the day or at night when lights are on. Use insect repellent day and night. When possible, wear long sleeves and pants. Check that window and door screens are secure and repair any holes. If possible, use air conditioning.

If someone in your home has dengue, take extra steps to prevent mosquitoes from biting the patient and then spreading dengue by biting others. Sleep under mosquito netting.

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